sidef/scripts/langton_s_ant_2.sf

#!/usr/bin/ruby

# Sidef implementation of Langton's Ant
# Translation of: https://rosettacode.org/wiki/Langton%27s_ant#Perl

# Using screen coordinates - 0,0 in upper-left, +X right, +Y down -
# these directions (right, up, left, down) are counterclockwise
# so advance through the array to turn left, retreat to turn right
var dirs = [[1,0], [0,-1], [-1,0], [0,1]];
var size = 15;

# we treat any false as white and true as black, so undef is fine for initial all-white grid
var plane = [];
for (0 .. size-1) {|i| plane[i] = [] };

# start out in approximate middle
var (x, y) = (size/2, size/2);

# pointing in a random direction
var dir = dirs.len.rand.int;

var move;
for (move = 0; (x >= 0) && (x < $size) && (y >= 0) && (y < size); move++) {

  # toggle cell's value (white->black or black->white)
  if (plane[x][y] = (1 - (plane[x][y] := 0))) {
        # if it's now true (black), then it was white, so turn right
        dir = ((dir - 1) % dirs.len);
  } else {
        # otherwise it was black, so turn left
        dir = ((dir + 1) % dirs.len);
  }

  x += dirs[dir][0];
  y += dirs[dir][1];
}

{
    "Out of bounds after %d moves at (%d, %d)\n".printf(move, x, y);
    for (var y=0; y < size; y++) {

        for (var x=0; x < size; x++) {
            print (plane[x][y] := 0 == 1 ? '#' : '.');
        }

        print "\n";
    }
}.run;